Lateral interbody fusion procedures are currently indicated for patients with ≤grade 1 spondylolisthesis. However, correction from the lateral approach is currently limited to regaining height and lordosis with only a low degree of spondylolisthesis correction, as the straight or lordotic cage is impacted during insertion to expand the disc space. Significant spondylolisthesis reduction is currently accomplished via a posterior approach with supplemental posterior fixation devices, including facet screws, translaminar screws, pedicle screws and rods, as well as intraspinous process devices or plates.
Although current lateral cages are characterized by symmetric superior and inferior geometries, the normal and degenerated discs do not have such similar superior and inferior endplate geometries. The lack of conformity of the cage endplate to the pertinent vertebral body can promote cage malpositioning during insertion, improper load balancing, increased settling and/or subsidence, as well as device movement following implantation.
Some surgeons using lateral cages attach lateral plating to the cage to achieve enhanced cage securement accompanied by some degree of biomechanical stabilization. However, most currently available lateral cages do not provide for plate attachment.
US 2004-0220668 (Eisermann) discloses a method for correcting spondylolisthesis from the lateral approach is provided in which a pair of insertion members are inserted laterally into upper and lower vertebrae, a connecting member is affixed to the insertion members, and a rotating force is applied to the connecting member to encourage the upper and lower vertebrae into a desired position relative to one another. In FIG. 9-11 of Eisermann, in an alternative embodiment, a slidable prosthetic joint can be used to help with the lateral approach for treating spondylolisthesis. The sliding joint extends generally along the longitudinal axis and includes a first slidable component and a second slidable component. The slidable components cooperate to form the sliding joint which is sized and configured for disposition within an intervertebral space between adjacent vertebral bodies. The sliding joint provides movement between the adjacent vertebral bodies to maintain or restore some of the motion similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, the slidable components are permitted to translate relative to one another in the axial plane.
US Patent Publication No. 2010-0016968 (Moore) discloses an apparatus and method that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain the new position. The implant has two halves which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by external set screw and internal locking block within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra by the disclosed method. The set screws are used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The correct position of the vertebrae is locked in place through a bolt and a plate.
U.S. Pat. No. 6,342,074 (Simpson) discloses a spinal fusion implant and method for maintaining proper lumbar spine curvature and intervertebral disc spacing where a degenerative disc has been removed. The one-piece implant comprises a hollow body having an access passage for insertion of bone graft material into the intervertebral space after the implant has been affixed to adjacent vertebrae. The implant provides a pair of screw-receiving passages that are oppositely inclined relative to a central plane. In one embodiment, the screw-receiving passages enable the head of an orthopedic screw to be retained entirely within the access passage. A spinal fusion implant embodied in the present invention may be inserted anteriorally or laterally. FIG. 4 discloses a device having fixtures for attaching to a lateral side of a vertebral body.
U.S. Pat. No. 6,878,167 (Ferree) discloses an osteotomy of a portion of a vertebral endplate and/or vertebral body allowing for easier insertion of a device that fits tightly into a disc space. It also discloses a mechanical device to hold the osteotomized portion of the vertebra against the vertebral body after the intradiscal device is placed. The device may be removed after the pieces of vertebra heal and fuse together. It further discloses a device secured to a side of the vertebral body in FIG. 4C.
The lateral access approach is frequently utilized to deliver interbody fusion cages to the lumbar spine. In comparison to conventional anterior or posterior approaches to the lumbar spine, the lateral approach is thought to minimize posterior and/or anterior tissue damage as well as reduce surgery time, associated blood loss, and infection risk.
When multi-level access to the spine is provided through a single minimal access port, the insertion trajectory to the superior and inferior levels is not parallel to those levels. In addition, direct lateral access parallel to the L4/5 and L5/S1 levels is prevented by the presence of the iliac crest.
Accordingly, the angled trajectory required for lateral access to these lower levels requires the cages to be implanted at a “malpositioned” angle that prevents balanced loading across the vertebral endplates and spine. See FIG. 1. This “malpositioned” access, associated endplate damage and device placement can initiate subsidence and spinal instability.
Current spreader and shaver technology includes varying paddle shapes and cutting geometries with rigid drive shafts. US Patent Publication No. 2008-00445966 discloses a chisel cutting guide for excising a portion of a vertebral body.
Conventional dilation systems used in intervertebral fusion procedures are typically rigid and non-steerable. Accordingly, they require a line of sight insertion towards the target disc.
US Patent Publication No. US 2007-0225815 (Annulex) discloses a curved stylet for steering within a disc space Annulex does not disclose an assembly comprising a curved guide wire and a flexible dilator tube.